Parkinson
Parkinson's disease is a brain disorder that leads to shaking, stiffness, and difficulty with walking, balance, and coordination. Parkinson's symptoms usually begin gradually and get worse over time. As the disease progresses, people may have difficulty walking and talking.

Alzheimer disease
Alzheimer's disease is a progressive disorder that causes brain cells to waste away (degenerate) and die. Alzheimer's disease is the most common cause of dementia — a continuous decline in thinking, behavioural and social skills that disrupts a person's ability to function independently.

Causes :- The abnormal build-up of proteins in and around brain cells. One of the proteins involved is called amyloid, deposits of which form plaques around brain cells. The other protein is called tau, deposits of which form tangles within brain cells.

Loss of memory or Amnesia
Memory loss (amnesia) is unusual forgetfulness. You may not be able to remember new events, recall one or more memories of the past, or both. The memory loss may be for a short time and then resolve (transient). Or, it may not go away, and, depending on the cause, it can get worse over time.